Liquid storage tank and gas holder



March 19, 1957 J. H. WIGGINS LIQUID STORAGE TANK AND GAS HOLDER 2Sheets-Sheet 1 Filed May 12, 1953 INVENTOR, JOHN H. WIGGIMS, BY 4M6 6 AT'TORNEY.

March 19, 1957 J. H. WIGGINS v LIQUID STORAGE TANK AND GAS HOLDER 2Sheets-Sheet 2 Filed May 12, 1953 INVENTOR. JOHN Hwwemls, M ATTORNEY.

LIQUlD STORAGE TANK AND GAS HOLDER John H. Wiggins, Chicago, Ill.

Application May 12, 1953, Serial No. 354,527

6 Claims. (Cl. 220-85) This invention relates to liquid storage tanksand gas holders, and particularly apparatus of the kind that comprise atank adapted to hold volatile liquids, and a gas holder mounted on saidtank and provided with a gas and vapor storage chamber whose top Wallcan move vertically, upwardly and downwardly, so as to vary the internalvolume of the storage chamber of the gas holder which is located aboveand in direct communication with the interior of the liquid tank so asto permit gases and vapors evolved from the liquid stored in the tank toexpand and pass into the storage chamber of the gas holder, and alsopermit condensate produced in the gas holder to return to the body ofliquid stored in the tank. While I have herein illustrated my inventionembodied in a combined liquid tank and gas holder, 1 wish it to beunderstood that my invention is applicable to gas holders that are usedsolely for storing gases and also gas holders of the kind used in vaporbalancing systems for volatile oil tanks, wherein the storage chamber ofa gas holder is connected by conduits with a plurality of tanks thathold volatile oil so that vapors evolved from the oil in the said tanksduring the day time can accumulate in the storage chamber of the gasholder and thereafter during the night, said gases can be fed back tothe oil tanks.

' My invention has for its main object, to reduce the cost, improve theoperation and reduce the overall height of apparatus of the kind thatconsist of a piston type, dry seal gas holder mounted on and supportedby a liquid storage tank.

Another object is to reduce or minimize the possibility of error orinaccuracy in the operation of gaging the liquid in a combined gasholder and liquid tank of the kind just referred to, and

Still another object of my invention is to provide a gas holder pistonof novel design that is particularly adapted for use in large size gasholders having storage chambers of relatively great diameters. Otherobjects and desirable features of my invention will hereafter be pointedout.

Figure 1 of the drawings is a vertical, transverse sectional view of acombined gas holder and liquid tank constructed in accordance with myinvention.

Figure 2 is a top plan view with portions of the weather roof of the gasholder broken away so as to more clearly illustrate the construction ofthe piston, and

Figure 3 is a vertical, transverse sectional view illustrating a designor type of construction particularly adapted for use in apparatus inwhich the piston of the gas holder is of relatively small diameter.

In the accompanying drawings which illustrate the preferred form of myinvention, the reference character A designates, as an entirety, a tankthat is adapted to hold liquid, usually oil from which gases and vaporsare evolved in the day time due to the tank becoming heated by the inited tteS atent suns rays, B designates a gas holder mounted on andsupported by said tank, C designates a vertically movable piston thatforms the top wall of the gas and vapor storage chamber of said gasholder, D designates a counterweighting mechanism attached to saidpiston C and designed so as to equal or be slightly greater than all ofthe dead weight of the piston and the fabric seal and other partsattached to or carried by the piston and E designates an annular backstop member attached to the lower end portion of the side wall of thegas holder and extending downwardly into the liquid tank A so as to forman abutment surface against which the fabric sealing element for thepiston bears in certain positions of the piston.

The tank A has a bottom 3, a cylindrical sidewall 2, a partial roof 1 ofannular form attached to the top edge of the tank side wall 2 andprojecting inwardly from same as shown in Figure 1 and a supportingstructure for said roof portion 1 composed of an annular row of posts 4on the interior of the tank attached at their upper ends to roof rafters5 whose outer ends are attached to the tank side wall 2. Also the tank Ais provided with a pressure relief valve and a vacuum re-. lief valve,not shown, which valves may be of conventional construction andoperation.

The gas holder B is provided with an annular side wall 6 that ispreferably attached to the inner edge of the roof portion 1 of the tankin vertical alignment with the roof supporting posts 4, and a weatherroof 7 is at tached to the top edge of said side wall 6 so as to protectthe piston C of the gas holder from rain, snow and the like, saidweather roof being supported by trusses or beam-s 8 attached at theirouter ends to the side wall 6. The piston C is of novel construction andis adapted for use in any kind of piston type gas holder where it isessential or desirable that the piston be of relatively great diameter,of stiii construction and of minimum weight. My improved piston inaddition to having the above mentioned desirable characteristics is easyto fabricate and it is of relatively small overall height ordepth,

thereby making it particularly adapted for use in a combined liquid tankand gas holder of the type or kind in which the piston, at times, movesdownwardly into close proximity or touching engagement with the liquidstored in the tank. The piston C is fabricated from metal plates and inthe form of my invention shown in Figure 1 consists of a diaphragmprovided with a dish shaped or concavo-convex central portion 11 whoseouter perimeter merges into a substantially flat, annular peripheralportion 1%? whose outer edge is attached to a stifl or rigid reinforcingmember 9 of annular form, the central portion 11 of the piston beingarranged with its convex surface presented downwardly. A beam andcompression member 12 is attached to the top side of the pistonpreferably at the point where the flat peripheral portion 10 merges intothe curved central portion 11, and inclined tension and strut membersare preferably used to tie the top edge portion of the beam 12 to thetwo portions 14) and 11 of the piston located outside of and inside ofsaid beam 12. Thus as shown in Figure 1 there is a group of inclinedtension and strut members 13 attached to the top edge portion of thebeam 12 and to the outer edge of the flat peripheral portion 10 of thepiston and there is a group of inclined tension and strut members 14attached to the top portion of the beam 12 and to the dished centralportion of the piston at a point some distance inwardly from theperimeter of said dished portion. The beam 12 extends circumferentiallyaround the piston as illustrated in Figure 2 and is herein shown asbeing-of annular form but it could be of other shape or outline.

The counterbalancing mechanism D for the piston C comprises two pairs ofchains or cables 15 attached to the top edge of the beam 12 in spacedrelation around the circumference of same, said cables leading upwardlyfrom said beam over sheaves or pulleys mounted on the weather roof 7 ofthe gas holder and the annular roof portion 1 of the tank, and thencedownwardly to counterbalance weights 19 located on the exterior of theside Wall 2 of the tank. In the counterbalancing mechanism herein shownone pair of said cables are attached to the beam '12 adjacent oppositeends of onediameter of the piston and lead to a single weight 19 towhich both cables are attached, and the other pairof cables are attachedto said beam adjacent opposite ends of the other diameter of the pistonand lead to a single weight 19 to which both of said cables areattached'as shown in Figure 2. Said cablespass over four single sheavesor pulleys 16 mounted on the top side of the weather roof 7 inapproximately direct vertical alignment with the beam member 12. Eachpair of said cables also passes over one double sheave or pulley 17mounted on the edge portion of the roof 7 in alignment with the sidewall 6 of the gas holder and one double sheave or pulley 18 mounted atthe outer edge of the roof portion 1 of the liquid tank directly abovethe side wall 2 of said tank. One advantage gained by mounting thesheaves 18 on the tank at the upper end of the tank side, is that alarge portion of the counterweight load is taken olf the posts 4 andrafters 5 that support the annular roof portion 1 of the tank. However,the main advantage of a counter-weighting mechanism of the constructionabove described is that ample room or space is provided for the verticaltravel of the weights 19 not withstanding the fact that the piston movesdownwardly a considerable distance below the bottom edge of the sidewall 6 of the gas holder. In other words, if the sheaves 18 were omittedand the weights 19 were hung from the sheaves 17 at the upper end of theside wall 6 of the gas holder, there would not be sufiicient room toprovide for the vertical travel of said weights, due to the fact thatsaid side wall 6 is mounted on the roof portion 1 of the tank and is nothigh or deep enough to provide for sufiicient travel of the weights topermit the piston to move downwardly to a point below the bottom edge ofthe side-wall 6' of the gas holder unless movable pulleys were rigged upwith the pulleys 17 so as to move only half the Vertical distance oftravel of the piston. Such a construction would be more complicated andexpensive than my improved mechanism, and it would necessitate the useof counterweights of double the mass or weight of the counterweights 19of my mechanism.

The space between the piston and the side wall 6 of the gas holder issealed by a flexible, curtain like sealing element 21 made of gas tightfabric. Said sealing element is of annular shape or form in generaloutline and is attached at its inner and outer edges to the piston andto the side wall 6 of the gas holder. It is of sufiicient area orfullness to permit the piston to move upwardly until the top edge of thebeam 12 on the piston comes into engagement with the supportingstructure for the'weather roof 7 of the gas holder, and move downwardlya certain distance into the tank A into close proximity or touchingengagement with the surface 22 of the liquid as indicated by the brokenline C in Figure 1. In order to back up the sealing element 21 andabsorb strains to which it is subjected when the tank is under a minuspressure, an annular back stop or abutment surface E is attached to thelower end portion of the side wall 6 of the gas holder so as to form, ineffect, an extension on said side wall that projects downwardly into thetank A. Said back stop E may be formed from metal plates or from aplurality orhorizontally disposed annular members 20 ar ranged insuperimposed, spacedrelation. When the piston appfoa-clie's'theend ofits downward stroke, the sealing element 21 arrests the downwardmovement of the piston and holds it suspended from the side wall 6 ofthe gas holder.

Figure 3 illustrates another embodiment of my invention in which the.side wall 6 of the gas holder is of sufficiently small diameter toovercome the necessity of attaching an annular compression and beammember and tension and compression struts to the top side of the piston.In such a structure it is practicable to attach the cables of thecounterbalancing mechanism to a center plate 24 arranged above thepiston and connected with the peripheral portion of the piston byinclined tension members 23. a

In an apparatus of the construction shown in Figure l, thecounterweighting mechanism lifts the piston C and the sealing element 21attached to the piston, so normally operates at say 0.03" vacuum at thetop and increasing to about 0.10" vacuum when the piston is being pulleddown near the end of its downward stroke. At empty the piston stops andis prevented from descending further into the tank by vertical tensionin the sealing element 21.

against the back stop or abutment surface 20.

tank then opens and provides pressure relief for the tank. Said vacuumvent may be set at 0.5 H20. When the piston moves upwardly the member 12on the top side of the piston engages the roof supporting structure ofthe gas holder and pressure will then build up until the pressure vent(not shown) on the roof 1 of the tank opens and provides pressure relieffor the tank. Said pressure vent may be .set at plus 1 H2O. The vacuumshows about how much tension the sealing element will have to supportwhen the piston is hanging from said sealing element, and the vacuumVent on the tank opens. piston counterweights create 0.1" H20 vacuum atthe bottom of the piston stroke and the vent valve opens at 0.5" H20vacuum, then the excess vacuum at that time is 0.5" minus 0.1" or 0.4H20 vacuum. The pressure shows: If the valve opens at 1" H20 and thepiston weighs 0.7" H20, then the net uplift on the piston is l.0"0.7 or0.3" H20 pressure which the struts 13 and 14 have to overcome incompression. At all times when not under positive pressure, the strutmembers 13 and 14 are under tension. When the pressure vent of the tankis open, the uplift of the gas in the tank may be greater than theweight of the piston and hence the strut members13 and '14 will thentake compression. The flat peripheral portion 10 of the piston can beabout 30% of the total area of the piston and the area bounded by thecircle of attachment of strut members 14 to the piston and beam member12 can also be about 30% of the total piston area. Thus these two 30%areas of the piston hang on the beam 12 and the tensions of 13 balancethe tensions of 14 and hence there is no accumulation of compression inthe top portion of beam 12, due to supporting area 10 of the piston andpart of area 11. This then leaves only about 40% of the total area ofthe piston to be carried by simple compression applied to the bottom ofbeam 12 by the dished portion 11 of the piston. Pressure forces exertedupon the two 30% areas are of course transmitted respectively to theupper portion of the beam 12 through the strut members 13 and 14 andproduce substantially equal torsional (beam twisting) moments about thecenter of the beam in opposite directions. Since these moments aresubstantially equal, but'opposite in direction, they tend to balance andcounteract each other, thereby minimizing the torsional stresses towhich the beam will be subjected. In addition, the heavy member 12 whichalso acts as a circular beam between cable attachments, is greatlyshortened by placing it a substantial portion of the piston radiusinside the annular reinforcing member 9 attached to the peripheral edgeof, the piston.

The result of the above described arrangement of parts,

is that a great deal of fabrication, erection and steel is' If the savedin member 12. Still another desirable feature of a piston that isconstructed, shaped and mounted in the manner above described is thatwhen it approaches the end of its downward stroke, the convex shapedcentral portion 11 of the piston progressively engages the liquid in thetank instead of plunging into the liquid over its entire area, therebyincreasing the fullness the tank can have before expansion volume of thepiston is affected.

Due to the fact that the vertically movable top wall portion of thestorage chamber of the gas holder consists of the piston C which isconstructed entirely of steel, I am not limited at all as to how large adiameter said chamber may have. I prefer to make said chamber ofrelatively great diameter as this enables me to decrease the lift orrise of the piston for a given volume, it reduced the depth of the sidewall of the gas holder and hence the overall height of the apparatus,and it reduces the amount of expensive gas tight fabric used as thesealing element for the piston, thereby effecting a considerable savingin the cost of building the apparatus and also cutting down evaporationloss as there is always some loss of gasoline vapor through a fabricpiston sealing element by permeation. Still another advantage of myapparatus which is extremely desirable from an operation standpoint, isthat it eliminates for practical purposes, the possibility of error orinaccuracy in the operation of gaging the liquid in the tank. In myapparatus the piston of the gas holder is completely counterbalanced andpulls a very slight vacuum. Hence, when the gage hatch of the tank isopened, any excess vacuum that may be in the tank is immediatelyrelieved, the piston does not displace any liquid because the piston ismore than counterbalanced and does not float on the liquid or cause theliquid to be displaced due to the Weight of the piston. Suppose forexample the vacuum in the tank is 0.3 H20 when the gage hatch is opened.Immediately a very small volume of air flows through the hatch into thetank until the vacuum is reduced to 0.1 H20 vacuum which is the amountcreated by the counter-weight of the piston. During gaging, air willcontinue to flow into the tank through the gaging hatch, but at such aslow rate at the 0.1 H20 vacuum for the couple of minutes required forgaging that there is no appreciable evaporation loss caused thereby.From the foregoing it will be seen that my improved structure has twooutstanding advantages as follows: first, no gaging error which isextremely important, and second practically no evaporation loss whilegaging through an open hole in the tank, due to the very smalldiiference in pressure inside the tank and the atmosphere.

Having thus described my invention, what I claim as new and desire tosecure by Letters Patent is:

1. In a gas holder, the combination of an annular side wall, a metalpiston arranged to move vertically within said side wall, a flexible,fabric sealing element for the piston attached to said side wall and tothe periphery of the piston, said piston having a substantially flat,horizontally disposed peripheral portion and a substantiallyconcavoconvex shaped central portion whose convexed side is disposeddownwardly, a substantially annular shaped reinforcing beam attached tothe top side of the piston at the point where the said peripheral andcentral portions of the piston merge, and oppositely inclined tensionand compression struts attached to the top edge of said beam and toportions of the piston lying at opposite sides of said beam.

2. A structure of the kind described in claim 1, which also includes acounter-weighting mechanism for the piston attached to the beam on thetop side of the piston.

3. A structure of the kind described in claim 1, wherein thesubstantially flat peripheral portion of the piston constitutesapproximately 30% of the total area of the piston and the saidoppositely inclined struts are so disposed that when they are intension, the tensions of the struts lying at one side of the beam on thetop side of the piston substantially balance the tensions of the strutslying at the opposite side of said beam.

4. An apparatus for storing liquids and gases, comprising a liquid tankprovided with a side wall and a partial roof of annular form attached toand projecting inwardly from the top edge of the tank side wall, a gasholder mounted on said tank and provided with an annular side wallattached to and projecting upwardly from the inner edge of the annularroof of the tank, a counter-weighted metal piston arranged to movevertically within the side Wall of the gas-holder and also to descendinto the tank, said piston having a substantially flat horizontallydisposed peripheral portion surrounding and merging into a substantiallyconcavo-convexed shaped central portion arranged with its convexedsurface disposed downwardly, a substantially circular beam attached tothe top side of the piston at approximately the point where saidperipheral and said central portions of said piston merge, a flexible,fabric sealing element for said piston attached to the piston and to theside Wall of the gas-holder and proportioned so that when the pistonmoves downwardly into the tank said sealing element arrests and limitsthe downward movement of the piston, and a stationary annular back stoparranged in the upper portion of the tank at a point below and invertical alignment with the side wall of the gas-holder so as to form anabutment surface for said fabric sealing element when said piston islocated inside the tank at a point lower than the annular roof of thetank, the counter-weighting mechanism for the piston comprising cablesthat are joined to said beam in spaced relation around the circumferenceof said beam.

5. In a gas-holder, the combination of an annular side wall, a metalpiston arranged to move vertically within said side wall, sealing meansabout the periphery of said piston cooperating with said side wall toprevent leakage of gas between said piston and said side wall, saidpiston having a substantially flat, horizontally disposed peripheralportion and a substantially concavo-convex shaped central portion whoseconvexed side is disposed downwardly, a substantially annular shapedreinforcing beam attached to the top side of the piston at the pointwhere the said peripheral and central portions of the piston merge, andoppositely inclined tension and compression struts attached to the topedge of said beam and to portions of the piston lying at opposite sidesof said beam.

6. In a storage tank for fluids having an upstanding substantiallycylindrical side wall, the combination comprising, a vertically movable,substantially circular, piston-like diaphragm disposed within the tankand providing a top wall for the fluid containing space in the tank,sealing means about the periphery of said diaphragm cooperating with theside Wall of the tank to prevent leakage of fluid between said diaphragmand the wall of the tank, an upstanding, rigid, annular reinforcing beamarranged concentrically upon said diaphragm and extending upwardlytherefrom, said beam dividing said diaphragm into a central portionencompassed by said beam and an annular peripheral portion extendingradially outwardly from said beam, said central portion of saidpiston-like diaphragm being concavo-convex in shape with its convexsurface disposed downwardly, a plurality of circumferentially spacedstruts extending diagonally upwardly from said peripheral portion ofsaid diaphragm to the upper portion of said beam whereby pressure forcesexerted upon said peripheral portion of said diaphragm will betransmitted to said beam and will produce a torsional moment thereaboutin a first direction, and a plurality of additional circumferentiallyspaced struts extending diagonally upwardly from the concave side ofsaid central portion of said diaphragm to the upper portion of said beamfor transmitting to said beam corresponding pressure forces exerted uponsaid central portion of said diaphragm so as to produce anothertorsional moment about said beam in the opposite direction, saidtorsional moments thereby tending to balance and counteract each otherto minimize the torsional stresses in saidbeam.

References Cited in the file of this patent UNITED STATES PATENTSTiifany Jan. 21, 1873 Pew Apr. 17, 1928 FOREIGN PATENTS France Mar. 4,1953

